v3.8.0.1
Employee Benefit Plans (Pension and Post Retirement Asset Allocations in Accordance with Investment Guidelines) (Details) - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]      
Notional $ 392,399 $ 366,091  
Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Total 13,655 12,861 $ 12,541
Net Value of investment of securities lending collateral invested in short-term bond 411 627  
Liability for securities lending collateral 411 627  
Pension Benefits | Equities | U.S.      
Defined Benefit Plan Disclosure [Line Items]      
Total 631 538  
Pension Benefits | Equities | International      
Defined Benefit Plan Disclosure [Line Items]      
Total 736 537  
Pension Benefits | Equities | Pooled separate accounts | U.S.      
Defined Benefit Plan Disclosure [Line Items]      
Total 552 472  
Pension Benefits | Equities | Pooled separate accounts | International      
Defined Benefit Plan Disclosure [Line Items]      
Total 365 269  
Pension Benefits | Equities | Common/collective trusts | U.S.      
Defined Benefit Plan Disclosure [Line Items]      
Total 79 66  
Pension Benefits | Equities | Common/collective trusts | International      
Defined Benefit Plan Disclosure [Line Items]      
Total 315 219  
Pension Benefits | Equities | United Kingdom insurance pooled funds | International      
Defined Benefit Plan Disclosure [Line Items]      
Total 56 49  
Pension Benefits | Fixed Maturities      
Defined Benefit Plan Disclosure [Line Items]      
Total 8,955 8,747  
Pension Benefits | Fixed Maturities | Pooled separate accounts      
Defined Benefit Plan Disclosure [Line Items]      
Total 1,357 1,283  
Pension Benefits | Fixed Maturities | Common/collective trusts      
Defined Benefit Plan Disclosure [Line Items]      
Total 509 441  
Pension Benefits | Fixed Maturities | Mortgage-backed      
Defined Benefit Plan Disclosure [Line Items]      
Total 1 1  
Pension Benefits | Fixed Maturities | Other U.S. government securities      
Defined Benefit Plan Disclosure [Line Items]      
Total 1,402 993  
Pension Benefits | Fixed Maturities | U.S. government securities (state & other)      
Defined Benefit Plan Disclosure [Line Items]      
Total 556 521  
Pension Benefits | Fixed Maturities | Non-U.S. government securities      
Defined Benefit Plan Disclosure [Line Items]      
Total 10 14  
Pension Benefits | Fixed Maturities | United Kingdom insurance pooled funds      
Defined Benefit Plan Disclosure [Line Items]      
Total 324 305  
Pension Benefits | Fixed Maturities | Corporate bonds      
Defined Benefit Plan Disclosure [Line Items]      
Total 3,622 4,039  
Pension Benefits | Fixed Maturities | Asset-backed      
Defined Benefit Plan Disclosure [Line Items]      
Total 5 7  
Pension Benefits | Fixed Maturities | Collateralized Mortgage Obligations      
Defined Benefit Plan Disclosure [Line Items]      
Total 492 506  
Pension Benefits | Fixed Maturities | Interest Rate Swaps      
Defined Benefit Plan Disclosure [Line Items]      
Total 12 9  
Pension Benefits | Fixed Maturities | Variable Life Insurance Policies      
Defined Benefit Plan Disclosure [Line Items]      
Total 47 39  
Pension Benefits | Fixed Maturities | Other      
Defined Benefit Plan Disclosure [Line Items]      
Total 618 589  
Pension Benefits | Fixed Maturities | Unrealized gain (loss) on investment of securities lending collateral      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Short-term Investments      
Defined Benefit Plan Disclosure [Line Items]      
Total 57 56  
Pension Benefits | Short-term Investments | Pooled separate accounts      
Defined Benefit Plan Disclosure [Line Items]      
Total 56 55  
Pension Benefits | Short-term Investments | United Kingdom insurance pooled funds      
Defined Benefit Plan Disclosure [Line Items]      
Total 1 1  
Pension Benefits | Real Estate      
Defined Benefit Plan Disclosure [Line Items]      
Total 1,149 1,037  
Pension Benefits | Real Estate | Pooled separate accounts      
Defined Benefit Plan Disclosure [Line Items]      
Total 714 666  
Pension Benefits | Real Estate | Partnerships      
Defined Benefit Plan Disclosure [Line Items]      
Total 435 371  
Pension Benefits | Other      
Defined Benefit Plan Disclosure [Line Items]      
Total 2,127 1,946  
Pension Benefits | Other | Partnerships      
Defined Benefit Plan Disclosure [Line Items]      
Total 706 551  
Pension Benefits | Other | Hedge Fund      
Defined Benefit Plan Disclosure [Line Items]      
Total 1,421 1,395  
Pension Benefits | NAV Practical Expedient      
Defined Benefit Plan Disclosure [Line Items]      
Total 2,562 2,317  
Pension Benefits | NAV Practical Expedient | Equities | Pooled separate accounts | U.S.      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | NAV Practical Expedient | Equities | Pooled separate accounts | International      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | NAV Practical Expedient | Equities | Common/collective trusts | U.S.      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | NAV Practical Expedient | Equities | Common/collective trusts | International      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | NAV Practical Expedient | Equities | United Kingdom insurance pooled funds | International      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | NAV Practical Expedient | Fixed Maturities | Pooled separate accounts      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | NAV Practical Expedient | Fixed Maturities | Common/collective trusts      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | NAV Practical Expedient | Fixed Maturities | Mortgage-backed      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | NAV Practical Expedient | Fixed Maturities | Other U.S. government securities      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | NAV Practical Expedient | Fixed Maturities | U.S. government securities (state & other)      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | NAV Practical Expedient | Fixed Maturities | Non-U.S. government securities      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | NAV Practical Expedient | Fixed Maturities | United Kingdom insurance pooled funds      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | NAV Practical Expedient | Fixed Maturities | Corporate bonds      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | NAV Practical Expedient | Fixed Maturities | Asset-backed      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | NAV Practical Expedient | Fixed Maturities | Collateralized Mortgage Obligations      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | NAV Practical Expedient | Fixed Maturities | Interest Rate Swaps      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | NAV Practical Expedient | Fixed Maturities | Variable Life Insurance Policies      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | NAV Practical Expedient | Fixed Maturities | Other      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | NAV Practical Expedient | Fixed Maturities | Unrealized gain (loss) on investment of securities lending collateral      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | NAV Practical Expedient | Short-term Investments | Pooled separate accounts      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | NAV Practical Expedient | Short-term Investments | United Kingdom insurance pooled funds      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | NAV Practical Expedient | Real Estate | Pooled separate accounts      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | NAV Practical Expedient | Real Estate | Partnerships      
Defined Benefit Plan Disclosure [Line Items]      
Total 435 371  
Pension Benefits | NAV Practical Expedient | Other | Partnerships      
Defined Benefit Plan Disclosure [Line Items]      
Total 706 551  
Pension Benefits | NAV Practical Expedient | Other | Hedge Fund      
Defined Benefit Plan Disclosure [Line Items]      
Total 1,421 1,395  
Pension Benefits | Level 1      
Defined Benefit Plan Disclosure [Line Items]      
Total 578 533  
Pension Benefits | Level 1 | Equities | Pooled separate accounts | U.S.      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 1 | Equities | Pooled separate accounts | International      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 1 | Equities | Common/collective trusts | U.S.      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 1 | Equities | Common/collective trusts | International      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 1 | Equities | United Kingdom insurance pooled funds | International      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 1 | Fixed Maturities | Pooled separate accounts      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 1 | Fixed Maturities | Common/collective trusts      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 1 | Fixed Maturities | Mortgage-backed      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 1 | Fixed Maturities | Other U.S. government securities      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 1 | Fixed Maturities | U.S. government securities (state & other)      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 1 | Fixed Maturities | Non-U.S. government securities      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 1 | Fixed Maturities | United Kingdom insurance pooled funds      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 1 | Fixed Maturities | Corporate bonds      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 1 | Fixed Maturities | Asset-backed      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 1 | Fixed Maturities | Collateralized Mortgage Obligations      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 1 | Fixed Maturities | Interest Rate Swaps      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 1 | Fixed Maturities | Variable Life Insurance Policies      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 1 | Fixed Maturities | Other      
Defined Benefit Plan Disclosure [Line Items]      
Total 578 533  
Pension Benefits | Level 1 | Fixed Maturities | Unrealized gain (loss) on investment of securities lending collateral      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 1 | Short-term Investments | Pooled separate accounts      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 1 | Short-term Investments | United Kingdom insurance pooled funds      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 1 | Real Estate | Pooled separate accounts      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 1 | Real Estate | Partnerships      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 1 | Other | Partnerships      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 1 | Other | Hedge Fund      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 2      
Defined Benefit Plan Disclosure [Line Items]      
Total 9,723 9,260  
Pension Benefits | Level 2 | Equities | Pooled separate accounts | U.S.      
Defined Benefit Plan Disclosure [Line Items]      
Total 552 472  
Pension Benefits | Level 2 | Equities | Pooled separate accounts | International      
Defined Benefit Plan Disclosure [Line Items]      
Total 365 269  
Pension Benefits | Level 2 | Equities | Common/collective trusts | U.S.      
Defined Benefit Plan Disclosure [Line Items]      
Total 79 66  
Pension Benefits | Level 2 | Equities | Common/collective trusts | International      
Defined Benefit Plan Disclosure [Line Items]      
Total 315 219  
Pension Benefits | Level 2 | Equities | United Kingdom insurance pooled funds | International      
Defined Benefit Plan Disclosure [Line Items]      
Total 56 49  
Pension Benefits | Level 2 | Fixed Maturities | Pooled separate accounts      
Defined Benefit Plan Disclosure [Line Items]      
Total 1,319 1,247  
Pension Benefits | Level 2 | Fixed Maturities | Common/collective trusts      
Defined Benefit Plan Disclosure [Line Items]      
Total 509 441  
Pension Benefits | Level 2 | Fixed Maturities | Mortgage-backed      
Defined Benefit Plan Disclosure [Line Items]      
Total 1 1  
Pension Benefits | Level 2 | Fixed Maturities | Other U.S. government securities      
Defined Benefit Plan Disclosure [Line Items]      
Total 1,402 993  
Pension Benefits | Level 2 | Fixed Maturities | U.S. government securities (state & other)      
Defined Benefit Plan Disclosure [Line Items]      
Total 556 521  
Pension Benefits | Level 2 | Fixed Maturities | Non-U.S. government securities      
Defined Benefit Plan Disclosure [Line Items]      
Total 10 14  
Pension Benefits | Level 2 | Fixed Maturities | United Kingdom insurance pooled funds      
Defined Benefit Plan Disclosure [Line Items]      
Total 324 305  
Pension Benefits | Level 2 | Fixed Maturities | Corporate bonds      
Defined Benefit Plan Disclosure [Line Items]      
Total 3,621 4,039  
Pension Benefits | Level 2 | Fixed Maturities | Asset-backed      
Defined Benefit Plan Disclosure [Line Items]      
Total 5 7  
Pension Benefits | Level 2 | Fixed Maturities | Collateralized Mortgage Obligations      
Defined Benefit Plan Disclosure [Line Items]      
Total 492 506  
Pension Benefits | Level 2 | Fixed Maturities | Interest Rate Swaps      
Defined Benefit Plan Disclosure [Line Items]      
Total 12 9  
Pension Benefits | Level 2 | Fixed Maturities | Variable Life Insurance Policies      
Defined Benefit Plan Disclosure [Line Items]      
Total 47 39  
Pension Benefits | Level 2 | Fixed Maturities | Other      
Defined Benefit Plan Disclosure [Line Items]      
Total 1 7  
Pension Benefits | Level 2 | Fixed Maturities | Unrealized gain (loss) on investment of securities lending collateral      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 2 | Short-term Investments | Pooled separate accounts      
Defined Benefit Plan Disclosure [Line Items]      
Total 56 55  
Pension Benefits | Level 2 | Short-term Investments | United Kingdom insurance pooled funds      
Defined Benefit Plan Disclosure [Line Items]      
Total 1 1  
Pension Benefits | Level 2 | Real Estate | Pooled separate accounts      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 2 | Real Estate | Partnerships      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 2 | Other | Partnerships      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 2 | Other | Hedge Fund      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Total 792 751  
Pension Benefits | Level 3 | Equities | Pooled separate accounts | U.S.      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 3 | Equities | Pooled separate accounts | International      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 3 | Equities | Common/collective trusts | U.S.      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 3 | Equities | Common/collective trusts | International      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 3 | Equities | United Kingdom insurance pooled funds | International      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 3 | Fixed Maturities | Pooled separate accounts      
Defined Benefit Plan Disclosure [Line Items]      
Total 38 36  
Pension Benefits | Level 3 | Fixed Maturities | Common/collective trusts      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 3 | Fixed Maturities | Mortgage-backed      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 3 | Fixed Maturities | Other U.S. government securities      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 3 | Fixed Maturities | U.S. government securities (state & other)      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 3 | Fixed Maturities | Non-U.S. government securities      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 3 | Fixed Maturities | United Kingdom insurance pooled funds      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 3 | Fixed Maturities | Corporate bonds      
Defined Benefit Plan Disclosure [Line Items]      
Total 1 0  
Pension Benefits | Level 3 | Fixed Maturities | Asset-backed      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 3 | Fixed Maturities | Collateralized Mortgage Obligations      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 3 | Fixed Maturities | Interest Rate Swaps      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 3 | Fixed Maturities | Variable Life Insurance Policies      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 3 | Fixed Maturities | Other      
Defined Benefit Plan Disclosure [Line Items]      
Total 39 49  
Pension Benefits | Level 3 | Fixed Maturities | Unrealized gain (loss) on investment of securities lending collateral      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 3 | Short-term Investments | Pooled separate accounts      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 3 | Short-term Investments | United Kingdom insurance pooled funds      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 3 | Real Estate | Pooled separate accounts      
Defined Benefit Plan Disclosure [Line Items]      
Total 714 666  
Pension Benefits | Level 3 | Real Estate | Partnerships      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 3 | Other | Partnerships      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Pension Benefits | Level 3 | Other | Hedge Fund      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Total 1,615 1,531 $ 1,584
Other Postretirement Benefits | Equities | U.S.      
Defined Benefit Plan Disclosure [Line Items]      
Total 789 676  
Other Postretirement Benefits | Equities | International      
Defined Benefit Plan Disclosure [Line Items]      
Total 216 186  
Other Postretirement Benefits | Equities | Common/collective trusts | U.S.      
Defined Benefit Plan Disclosure [Line Items]      
Total 182 170  
Other Postretirement Benefits | Equities | Common/collective trusts | International      
Defined Benefit Plan Disclosure [Line Items]      
Total 110 96  
Other Postretirement Benefits | Equities | Equities | U.S.      
Defined Benefit Plan Disclosure [Line Items]      
Total 2    
Other Postretirement Benefits | Equities | Variable Life Insurance Policies | U.S.      
Defined Benefit Plan Disclosure [Line Items]      
Total 605 506  
Other Postretirement Benefits | Equities | Variable Life Insurance Policies | International      
Defined Benefit Plan Disclosure [Line Items]      
Total 106 90  
Other Postretirement Benefits | Fixed Maturities      
Defined Benefit Plan Disclosure [Line Items]      
Total 553 555  
Other Postretirement Benefits | Fixed Maturities | Common/collective trusts      
Defined Benefit Plan Disclosure [Line Items]      
Total 52 59  
Other Postretirement Benefits | Fixed Maturities | Other U.S. government securities      
Defined Benefit Plan Disclosure [Line Items]      
Total 87 78  
Other Postretirement Benefits | Fixed Maturities | Non-U.S. government securities      
Defined Benefit Plan Disclosure [Line Items]      
Total 2 2  
Other Postretirement Benefits | Fixed Maturities | Corporate bonds      
Defined Benefit Plan Disclosure [Line Items]      
Total 151 176  
Other Postretirement Benefits | Fixed Maturities | Asset-backed      
Defined Benefit Plan Disclosure [Line Items]      
Total 28 49  
Other Postretirement Benefits | Fixed Maturities | Collateralized Mortgage Obligations      
Defined Benefit Plan Disclosure [Line Items]      
Total 29 27  
Other Postretirement Benefits | Fixed Maturities | Other collateralized loans      
Defined Benefit Plan Disclosure [Line Items]      
Total 30    
Other Postretirement Benefits | Fixed Maturities | Interest Rate Swaps      
Defined Benefit Plan Disclosure [Line Items]      
Total   1  
Other Postretirement Benefits | Fixed Maturities | Variable Life Insurance Policies      
Defined Benefit Plan Disclosure [Line Items]      
Total 163 157  
Other Postretirement Benefits | Fixed Maturities | Other      
Defined Benefit Plan Disclosure [Line Items]      
Total 11 6  
Other Postretirement Benefits | Short-term Investments      
Defined Benefit Plan Disclosure [Line Items]      
Total 57 114  
Other Postretirement Benefits | Short-term Investments | Registered investment companies      
Defined Benefit Plan Disclosure [Line Items]      
Total 57 114  
Other Postretirement Benefits | NAV Practical Expedient      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | NAV Practical Expedient | Equities | Common/collective trusts | U.S.      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | NAV Practical Expedient | Equities | Common/collective trusts | International      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | NAV Practical Expedient | Equities | Equities | U.S.      
Defined Benefit Plan Disclosure [Line Items]      
Total 0    
Other Postretirement Benefits | NAV Practical Expedient | Equities | Variable Life Insurance Policies | U.S.      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | NAV Practical Expedient | Equities | Variable Life Insurance Policies | International      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | NAV Practical Expedient | Fixed Maturities | Common/collective trusts      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | NAV Practical Expedient | Fixed Maturities | Other U.S. government securities      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | NAV Practical Expedient | Fixed Maturities | Non-U.S. government securities      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | NAV Practical Expedient | Fixed Maturities | Corporate bonds      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | NAV Practical Expedient | Fixed Maturities | Asset-backed      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | NAV Practical Expedient | Fixed Maturities | Collateralized Mortgage Obligations      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | NAV Practical Expedient | Fixed Maturities | Other collateralized loans      
Defined Benefit Plan Disclosure [Line Items]      
Total 0    
Other Postretirement Benefits | NAV Practical Expedient | Fixed Maturities | Interest Rate Swaps      
Defined Benefit Plan Disclosure [Line Items]      
Total   0  
Other Postretirement Benefits | NAV Practical Expedient | Fixed Maturities | Variable Life Insurance Policies      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | NAV Practical Expedient | Fixed Maturities | Other      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | NAV Practical Expedient | Short-term Investments | Registered investment companies      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | Level 1      
Defined Benefit Plan Disclosure [Line Items]      
Total 63 115  
Other Postretirement Benefits | Level 1 | Equities | Common/collective trusts | U.S.      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | Level 1 | Equities | Common/collective trusts | International      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | Level 1 | Equities | Equities | U.S.      
Defined Benefit Plan Disclosure [Line Items]      
Total 0    
Other Postretirement Benefits | Level 1 | Equities | Variable Life Insurance Policies | U.S.      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | Level 1 | Equities | Variable Life Insurance Policies | International      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | Level 1 | Fixed Maturities | Common/collective trusts      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | Level 1 | Fixed Maturities | Other U.S. government securities      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | Level 1 | Fixed Maturities | Non-U.S. government securities      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | Level 1 | Fixed Maturities | Corporate bonds      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | Level 1 | Fixed Maturities | Asset-backed      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | Level 1 | Fixed Maturities | Collateralized Mortgage Obligations      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | Level 1 | Fixed Maturities | Other collateralized loans      
Defined Benefit Plan Disclosure [Line Items]      
Total 0    
Other Postretirement Benefits | Level 1 | Fixed Maturities | Interest Rate Swaps      
Defined Benefit Plan Disclosure [Line Items]      
Total   0  
Other Postretirement Benefits | Level 1 | Fixed Maturities | Variable Life Insurance Policies      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | Level 1 | Fixed Maturities | Other      
Defined Benefit Plan Disclosure [Line Items]      
Total 6 1  
Other Postretirement Benefits | Level 1 | Short-term Investments | Registered investment companies      
Defined Benefit Plan Disclosure [Line Items]      
Total 57 114  
Other Postretirement Benefits | Level 2      
Defined Benefit Plan Disclosure [Line Items]      
Total 1,543 1,405  
Other Postretirement Benefits | Level 2 | Equities | Common/collective trusts | U.S.      
Defined Benefit Plan Disclosure [Line Items]      
Total 182 170  
Other Postretirement Benefits | Level 2 | Equities | Common/collective trusts | International      
Defined Benefit Plan Disclosure [Line Items]      
Total 110 96  
Other Postretirement Benefits | Level 2 | Equities | Equities | U.S.      
Defined Benefit Plan Disclosure [Line Items]      
Total 2    
Other Postretirement Benefits | Level 2 | Equities | Variable Life Insurance Policies | U.S.      
Defined Benefit Plan Disclosure [Line Items]      
Total 605 506  
Other Postretirement Benefits | Level 2 | Equities | Variable Life Insurance Policies | International      
Defined Benefit Plan Disclosure [Line Items]      
Total 106 90  
Other Postretirement Benefits | Level 2 | Fixed Maturities | Common/collective trusts      
Defined Benefit Plan Disclosure [Line Items]      
Total 52 59  
Other Postretirement Benefits | Level 2 | Fixed Maturities | Other U.S. government securities      
Defined Benefit Plan Disclosure [Line Items]      
Total 87 78  
Other Postretirement Benefits | Level 2 | Fixed Maturities | Non-U.S. government securities      
Defined Benefit Plan Disclosure [Line Items]      
Total 2 2  
Other Postretirement Benefits | Level 2 | Fixed Maturities | Corporate bonds      
Defined Benefit Plan Disclosure [Line Items]      
Total 151 176  
Other Postretirement Benefits | Level 2 | Fixed Maturities | Asset-backed      
Defined Benefit Plan Disclosure [Line Items]      
Total 28 48  
Other Postretirement Benefits | Level 2 | Fixed Maturities | Collateralized Mortgage Obligations      
Defined Benefit Plan Disclosure [Line Items]      
Total 27 22  
Other Postretirement Benefits | Level 2 | Fixed Maturities | Other collateralized loans      
Defined Benefit Plan Disclosure [Line Items]      
Total 28    
Other Postretirement Benefits | Level 2 | Fixed Maturities | Interest Rate Swaps      
Defined Benefit Plan Disclosure [Line Items]      
Total   1  
Other Postretirement Benefits | Level 2 | Fixed Maturities | Variable Life Insurance Policies      
Defined Benefit Plan Disclosure [Line Items]      
Total 163 157  
Other Postretirement Benefits | Level 2 | Fixed Maturities | Other      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | Level 2 | Short-term Investments | Registered investment companies      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Total 9 11  
Other Postretirement Benefits | Level 3 | Equities | Common/collective trusts | U.S.      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | Level 3 | Equities | Common/collective trusts | International      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | Level 3 | Equities | Equities | U.S.      
Defined Benefit Plan Disclosure [Line Items]      
Total 0    
Other Postretirement Benefits | Level 3 | Equities | Variable Life Insurance Policies | U.S.      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | Level 3 | Equities | Variable Life Insurance Policies | International      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | Level 3 | Fixed Maturities | Common/collective trusts      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | Level 3 | Fixed Maturities | Other U.S. government securities      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | Level 3 | Fixed Maturities | Non-U.S. government securities      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | Level 3 | Fixed Maturities | Corporate bonds      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | Level 3 | Fixed Maturities | Asset-backed      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 1  
Other Postretirement Benefits | Level 3 | Fixed Maturities | Collateralized Mortgage Obligations      
Defined Benefit Plan Disclosure [Line Items]      
Total 2 5  
Other Postretirement Benefits | Level 3 | Fixed Maturities | Other collateralized loans      
Defined Benefit Plan Disclosure [Line Items]      
Total 2    
Other Postretirement Benefits | Level 3 | Fixed Maturities | Interest Rate Swaps      
Defined Benefit Plan Disclosure [Line Items]      
Total   0  
Other Postretirement Benefits | Level 3 | Fixed Maturities | Variable Life Insurance Policies      
Defined Benefit Plan Disclosure [Line Items]      
Total 0 0  
Other Postretirement Benefits | Level 3 | Fixed Maturities | Other      
Defined Benefit Plan Disclosure [Line Items]      
Total 5 5  
Other Postretirement Benefits | Level 3 | Short-term Investments | Registered investment companies      
Defined Benefit Plan Disclosure [Line Items]      
Total $ 0 $ 0